Dear GothM940,

Hope you're well. There's no need to use sealers, when installing cat-back exhaust pipes. One can coat the pipe-ends with an anti-seize compound (high temperature), which eases removal, should that be needful.

However, a seal between the pipes is the result of proper tightening of the clamps. Thus, if "condensation" drips from pipe joints, the clamps need to be tightened. I'd go back to the shop that did the work. It should take them only a few minutes to tighten the clamps.

As to removing exhaust manifold, etc., I'd use a good quality penetrating oil (e.g., PB Blaster, Kroil, etc.) on all fasteners. These oils slowly penetrate micro-channels in the corrosion, and so weaken the corrosion bond. If possible, saturate each fastener daily, for several days in a row. That allows the oil plenty of time to do its work.

It is helpful to clean the ends of rusty studs with a wire brush. Cleaning rust on the stud-ends makes it easier for penetrating oil to work. A cleaned stud will offer less resistance to the nut, when you remove the nut. Anything that eases strain on the studs is worth doing. Removing a broken studen is never easy.

When removing heavily rusted fasteners (nuts or bolts), it is best to tighten then ever-so-slightly, before trying to remove them. That "tightening" helps to break the corrosion bond. The fastener need not move more than a couple of thousandths of an inch: so little, you might not notice it. But that slight movement can be enough to weaken or to break the corrosion bond.

Given the difficulty of replacing these gaskets, I'd use Volvo or Elring brand gaskets.

When re-assembling the system, I'd use a high-temperature (nickel-based) anti-seize compound on studs and bolts. This will ease removal, should that be needful.

Hope this helps.

Yours faithfully,

Spook